1. Field of the Invention
The present invention relates in general to an apparatus for interchanging floppy diskette drive (FDD) letter assignments in a computer system. In particular, the present invention provides an apparatus for interchanging floppy diskette drive assignments in a computer system that is independent of the operating system installed.
2. Description of Related Art
Floppy diskette drives for computers, although considered today to have a small data storage capacity and relatively slow read-write access, are still indispensable devices for modern microprocessor-based computer systems. One of the more important functions of a floppy diskette drive is to allow the computer to be booted to a particular operating system regardless of what system may be stored on a hard drive of the computer. This is particularly important during initial setup of the computer and during maintenance or repair.
Commercially available floppy diskette drives include, among others, the so-called mini-floppy diskette and micro-floppy diskette drives. The mini-floppy drive, which holds approximately 1.2M or 360K bytes, is more frequently referred to as the five-and-a-quarter-inch (5.25-in) drive, while the micro-floppy drive with a normal capacity of either 1.44M or 720K bytes is referred to as the three-and-a-half-inch (3.5-inch) drive. While 3.5-in drives are becoming more and more popular, there is still a considerable number of installed computer systems operating with 5.25-inch drives.
The co-existence of the two type of different diskette drives has caused some inconvenience in the use of floppy diskettes, both at the user and the software supplier ends. Most modern application software programs allow for the installation from either the A or B drive of a computer system, regardless of either the A drive is a 5.25 or a 3.5-inch drive, or vice versa. However, the installation, or maintenance and repair of operating system products require that the boot diskette be in the physical drive A. It is not unusual for a user to have at hand a copy of a software program that is distributed in 5.25-inch diskettes while the computer system to be used has a 3.5-inch floppy diskette drive installed as the physical drive A and a 5.25-in drive installed as drive B.
A computer user having a software package with a mis-matched drive A on the computer system has two ways to overcome the problem. Either the software package will have to be replaced with a version on a set of compatible floppy diskettes, or the A and B drive physical connection will have to be interchanged. Some users may not want to spend the time or money involved in the replacement of the software diskettes. On the other hand, the complexity involved in the interchange of the drives arrangement depends on the hardware design of the computer system.
Some computer systems have included in their firmware a drive swapping feature for swapping the drives. However, other systems require that the physical cable connection for the A and B drives be interchanged.
To physically interchange the connection of the floppy diskette drives in a computer system, the user must have sufficient knowledge of the interconnection for the floppy diskette subsystem. Not all users have this knowledge or the confidence to perform this drive swapping operation. For those users capable of implementing the interchange, the drive cable may not be sufficiently long to achieve the drive connection interchange.
Those computer systems with a firmware drive swapping feature do provide the apparent functionality of interchanging the drive letter arrangement. In other words, the drives physically installed in a computer system with one selected drive naming arrangement may be interchanged by executing a software routine. For example, in the IBM-compatible 80.times.86-based personal computer systems, the BIOS (basic input/output system) programs published by American Megatrends Incorporated of Norcross, Ga., U. S. A. provide a drive A-B swapping feature in the BIOS setup utility that allows for the swapping of a floppy drive physically installed as B to be "swapped" as the logical A drive in the system.
However, while such a drive swapping scheme prevents the need to actually change the cable connection inside the computer system unit, this scheme relies on the drive parameter modification in relation to the interrupt service routine (ISR) of the BIOS program in the computer system. For most application software programs that direct their floppy diskette drive accesses via the ISR, this works fine. With those other operating systems, such as Operating System/2 published by International Business Machines Corporation, this ISR-related drive swapping scheme is useless, because these operating system products bypass the ISR altogether when they access the floppy diskette drives.
On other occasions, there is also the need to interchange the drive assignment letters. For example, when drive A of a system fails, a interchanging capability would allow the swap of the other drive as the drive A on a temporary basis, before the failed drive is repaired or replaced.